The Subject
by iamtheriversong
Summary: Delta Thay, renegade Time Lord, currently working for UNIT. Well, that's what they tell people. It's really more of a hobby. But when a mission pops up that she just can't ignore, Delta finds herself whisked to Baker Street, to find an old enemy waiting in the shadows. Who!Lock AU in which Delta takes the place of the Doctor. Spans S3 and onward of Sherlock.
1. Beginnings

Delta Thay sat at her temporary desk at UNIT's base in Tower Bridge, a hand running through her long brown hair. Her emerald eyes scanned the screen of the laptop in front of her, a sigh escaping her her lips. She glanced down at the clock in the corner of the screen, finding it to be 3:37am. Delta groaned, tipping her head back and closing her eyes.

The sound of footsteps echoing ever closer stirred her, and she looked up to see a blonde woman standing in the doorway. She looked around 40, and held herself with an air of authority.

"Miss. Stewart." Delta acknowledged, nodding as the woman sat down in a chair.

"I tell you every time, Delta, you call me Kate. Any luck with the search?"

"It's hard to say. The flat below the subject is free, but it may cause suspicion. But I may be able to pull it off."

"How?"

"Deep cover. I've spent the last six hours creating a fake life."

Kate raised her eyebrows, signalling for Delta to continue with her hands.

"Eira Davies. Welsh, 19 years old. On a gap year from Oxford University, using the time to study at St Bartholomews hospital. Majoring in opthamology, psychology, literature and performing arts. Parents died in a car crash in America when she was seven, has been living with her grandmother who recently passed away. No other family."

Kate thought for a moment, before nodding.

"You leave at 6pm. Get some clothes and tie up the loose ends of the cover. I'll be there to see you off."

"Yes ma'am. I'll leave as soon as the shops open."

"Oh, and Delta."

"Yes?"

"Try not to let Mr. Holmes figure out what you're doing at Baker Street."

"Of course."


	2. Hello! I'm Eira

Delta leant her head against the window of her cab (it wasn't a real cab. But UNIT had made it look like one), the soft rain thrumming through her ears. The brakes screeched as they pulled to a stop outside of 221B, and Delta straightened up. She could see the outline of a man watching her from the second floor window, so leant forwards as if to pay the driver; instead giving him a chewing gum. The driver, James Trass, was a good friend, and smirked when he took the gum.

"Be careful Delta." He whispered,

"Oh, James, you know me. Never could keep away from trouble. Tell Kate I'll report back every 48 hours, as agreed."

"Will do ma'am."

"Thanks." Delta gave him a final smile, before grabbing the suitcase that was sat on the seat next to her, and pushing open the door. She strode up to the building, occasionally glancing to the man in the window discreetly, and knocked.

Delta looked down at her appearance, hoping it looked normal. She was wearing black skinny jeans, a black top, red converse and a red jacket (she liked to be colour coordinated). After a few seconds, the door swung open to reveal a woman who seemed to be in her late 50's.

"Mrs. Hudson?" Delta inquired, raising her eyebrows slightly.

"Yes, that's me. Can I help? Are you here for Sherlock?" Mrs. Hudson replied, motioning to the stairs when she mentioned Sherlock.

'Yeah, I've been sent by UNIT to spy on him.' Delta thought,

"It's Eira Davies. I contacted you this morning about the free flat? You said I could move in right away if I was happy with it."

"Oh, of course dear! Sorry, come in, you're getting wet!" Mrs. Hudson exclaimed, ushering Delta in.

"Thank you. I looked at the pictures you sent me, and it looks perfect." Delta replied, walking into the hallway as Mrs. Hudson lead her down it.

"Oh marvelous. But, why are you getting a flat so young?"

"I'm studying at St. Bart's. I'm on a gap year from Oxford. Needed somewhere in the city, and this is right in the hustle of it all."

"St Bart's? What are you studying?"

"Ophthalmology, Psychology, and literature. The literatures just for fun, though."

"Oh, that's lovely. Well, here it is." Mrs. Hudson unlocked the door she was in front of. It stood on the left of the hall, parallell to a different door. "My flat's just opposite, and at the end of the hall is the washing machines and dryers."

Delta nodded, walking into the flat. She looked around, pleased with the bargain she had gotten herself. Truth be told, the flat was amazing. Wooden floor, a brilliantly patterned wallpaper, and it looked to be a good size.

"So there's the bathroom through that hall, the bedrooms just to the left and has a door leading to the bathroom too. This is the main living space, and the kitchen is just through that door on your left." Mrs. Hudspon explained, standing in the doorway.

"It's even better than the pictures. I'll have it." Delta said, turning to face Mrs. Hudson. "I have the first three months rent with me. Well, if you'll take a cheque?"

"Oh, that's fine dear. You don't need to give it to me now, get settled in first."

"No, no, I must. Here." Delta insisted, pulling out a cheque from her pocket and holding it out. Mrs. Hudson looked from Deltas face to the check, sighed, and took the check.

"I'll leave you be now, just call if you need anything." Mrs. Hudson replied, turning to leave.

"Thank's." Delta nodded, smiling as Mrs. Hudson left, closing the door behind her. She pressed her forehead against the wood of the door, exhaling slowly. "Right then. Time to unpack."

Delta spun on her heels and made her way to the sofa, thumping her suitcase onto it. It was then she heard a knock at the door. Delta groaned, walked back to the door and opened it a crack.

The man waiting outside spoke immediately:

"Ah, hello. I'm John Watson. I'm a friend of the man who lives upstairs." Delta gave him a discreet once over, before replying

"Hello! I'm Eira."

**A/n:**  
**Hey guys! So, how'd you like the new story? I know Delta seems like a teenager, but she's posing as one so I'm just gonna say it's intentional. So, please review, and give it a vote or a like or whatever if you deem it worthy. I'm going to ask to get three votes before I post the next bit (though I'd probably post it anyway). See ya - tea-in-the-TARDIS**


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